The compound (I) is best known as Iopamidol, which is one of the world top compounds in the field of non-ionic X-ray contrast media.
The syntheses of Iopamidol known in literature, for instance the one described in GB 1472050, foresee a final purification at the end of the process, by using ion-exchange resins and successive recrystallization from EtOH or iso-PrOH.
Recently the patent application WO-A-95/04031 mentions different solvents (n-BuOH, sec-BuOH, iso-BuOH and/or t-BuOH) from which Iopamidol crystallizes. Butyl alcohols, especially 2-butanol, are used in a manner similar to that mentioned above for ethanol. It is claimed that butyl alcohols are more easily removed than ethanol from the final product in the drying step.
A more recent application EP-A-0 747 344 discloses the use of propanol or isopropanol as crystallization solvent to overcome the problem of the formation of pasty products during the crystallization.
Another recent application IT95A001429 discloses the use of monoether of the ethylenglycol (e.g. Cellosolve.RTM. or Metilcellosolve.RTM.) as crystallization solvent for Iopamidol. This procedure allows the crystallization of Iopamidol starting from a product with a purity grade comprised between 99-99.5%.